It is known to produce a sail of the laminated type of a triangular shape having three tops defining respectively three corners, that is, tack corner, head corner and clew corner, and three sides, respectively the foot or base of the sail, between the tack corner and the clew corner, the fore leech or reef, between the tack corner and the head corner, and the after leech, between the clew corner and the head corner.
The sail comprises a plurality of sailcloths joined together by means of stitching or gluing, each of which comprises in turn two outer covering layers, made of plastic material, between which reinforcement elements are positioned, made of carbon fiber. The latter are disposed following the force lines generated on the sail by the state of stress to which it is subjected during use. All together, the reinforcement elements achieve a main reinforcement structure for the sail.
It is also known to insert auxiliary reinforcement elements between the two outer covering layers of all the sailcloths, in order to achieve auxiliary reinforcement structures, for example with regular pre-formed grids or nets, or with bundles of threads angled with respect to the reinforcement threads disposed according to the aforesaid force lines and forming the main reinforcement structure, in order to support secondary forces, always present on the sail, and responsible for considerable deformations of the outer covering layer.
The state of stress acting on the sail is the sum of the stresses of an aerodynamic nature generated by the action of the wind on the surface of the sail, consisting of a field of pressures that varies from point to point, and of stresses imposed by the action of the crew on the sail in order to perform maneuvers, stresses that are transmitted to the sail at the points where the sail is constrained to the boat.
This state of stress is in itself very complex, as it is a function of the structure of the sail itself, and to determine it entails the need to solve what is commonly defined in the state of the art as an aero-elastic problem.
Making sails of a laminated type, where the force lines represent a kind of guide direction according to which the reinforcement elements are disposed, has the disadvantage, however, that the reciprocal position and orientation of the force lines vary continuously as the conditions of the wind vary and as the control lines or current maneuvers are adjusted (for example sheets, halyards, flying shrouds or other) by the crew, making it necessary, in practice, to choose one or more design points when designing the sail, and to distribute the reinforcement elements in a way which represents a compromise and is not the best possible solution.
Another disadvantage of sails made in this way is the increase in the number of auxiliary reinforcement elements, which therefore entails a considerable increase in the material used to make the sail, and hence of the weight of the sail.
The solution is also known of making a sail using reinforcement elements that are not disposed on the force lines.
According to this conventional solution, however, large size curved molds are used, which make the method to construct large size sails very inefficient from the economic point of view, and very laborious and complex.
It is also known to make sails by putting a large quantity of reinforcement elements at the points where the sail is constrained to the boat, neglecting the central zone of the sail, which on the contrary is fundamental in order to maintain its shape during use.
It is also known to make sails relying on curves having the same level of stress value, known as iso-stress curves. However, this approach also has the disadvantage that one force condition from among the infinite possibilities is chosen, and since, between one iso-stress curve and the next, the stress is not constant but continuously varies, a structure like the one proposed would in fact only be iso-stress if one were to have recourse to infinite iso-stress elements, something which is impossible in practice.
One purpose of the present invention is to achieve an apparatus and perfect a method to make a sail wherein the reinforcement elements are dependent directly on the state of stress to which the sail is subject, and not on the force lines acting on the sail, which are a consequence of said state of stress, with the purpose of guaranteeing a better maintenance and control of the shape, a greater strength and duration given the same weight with respect to other sails of the laminated type.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.